This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2001-304013, filed Sep. 28, 2001, the entire contents of which are incorporated herein by reference.
The present invention relates to an ultrasonic diagnostic apparatus capable of diagnosis with contrast echo method using contrast medium.
An ultrasonic apparatus can noninvasively obtain a tomographic image of soft tissues inside a living body from the surface of the body using reflection of an ultrasonic wave and has advantages such as compactness, low price, capability of real time imaging, increased safety due to a lack of X-ray dosing, capability of blood flow imaging, etc., when compared to other diagnostic devices, such as X-ray diagnostic apparatus, X-ray CT apparatus, MRI apparatus or nuclear medicine diagnostic apparatus, and the like. Because of such advantages, ultrasound is currently widely used in many medical fields such as cardiac medicine, abdominal medicines such as gastroenterology, urology, obstetrics, gynecology, as well as others.
There are a variety of imaging methods for the ultrasonic diagnostic apparatus. xe2x80x9cContrast Echoxe2x80x9d method is one of the important techniques to obtain an ultrasonic image in which scattered echo signals are enhanced by using an ultrasonic contrast medium containing microbubbles injected into a blood vessel of an object.
Recently, new contrast media for intravenous injection have emerged and imaging methods suitable for these contrast media have also been developed. For example, such methods include a Filter method (an imaging method using one pulse per scan line: U.S. Pat. No. 5,678,553), a Doppler method (an imaging method using more than two in-phase pulses per scan line), a Phase Inversion method (an imaging method using two 180xc2x0 out-of-phase pulses per scan line: U.S. Pat. No. 5,632,277), a Phase Inversion Doppler method (an imaging method using more than three pulses alternated by 180xc2x0 from pulse to pulse per scan line: U.S. Pat. No. 6,095,980), the contents of which are herein incorporated by reference.
When performing a Contrast Echo method with any of the above methods, conventionally ultrasonic waves with medium or high acoustic pressure, such as MI (mechanical index) value of more than 0.5 have been used. This is typically done to obtain a prominent contrast enhancement effect by collapsing the microbubbles in the contrast medium. For example, when using one of widely used contrast medium, Levovist, manufactured by Schering, the image may not be properly enhanced unless ultrasonic waves with high acoustic pressure, such as those having an MI value of more than 0.8 are used.
Transmission of ultrasonic waves with high acoustic pressure and the subsequent collapse of microbubbles greatly affects ultrasonic imaging. When an ultrasonic wave with high acoustic pressure is propagated through tissue, a harmonic component is generated in an echo. However, the above-mentioned Filter method or Phase Inversion method can not separate a harmonic component from tissues (hereinafter xe2x80x9cTHI componentxe2x80x9d) from a harmonic component from bubbles. Accordingly an image of bubbles obtained with the Filter method or the Phase Inversion method may not have enough contrast, and it may be difficult to distinguish between blood flow and a parenchymal contrast-enhancement in a contrast echo image.
Further, a collapse of bubbles creates a broadband echo signal when more than two ultrasonic beams are transmitted per scan line. This broadband echo signal, called a pseudo-Doppler signal, can be utilized to produce an image by suppressing tissue and THI components in the fundamental signal.
However, a color Doppler image based on the pseudo-Doppler signals would result in an image of thin blood vessels and contrast-enhancement in parenchyma with many aliasing points, which does not indicate proper blood flow velocities or directions unlike a normal Doppler signal. Therefore, in most cases when an ultrasonic image obtained with contrast echo method is displayed, power Doppler is used instead of color Doppler, which is generally suitable for showing blood flow velocity.
It is accordingly an aspect of the present invention to provide an ultrasonic diagnostic apparatus, including an image processing unit capable of producing an ultrasonic image from the echo signal, where each pixel in an ultrasonic image has a brightness and a color, each of which is adjusted according to information on blood flow in a subject. The ultrasonic beam used to generate the ultrasonic image is transmitted with a mechanical index value configured to collapse microbubbles to an extent that an echo signal contains the information on blood flow in an object used to adjust the brightness and the color.